IoT-Oriented Single-Transmitter Multiple-Receiver Wireless Charging Systems Using Hybrid Multi-Frequency Pulse Modulation

For Internet-of-Things (IoT) devices, battery life is always one of the most challenging technical issues. How to extend the working duration is always a concern for IoT in the premise of increasing no battery capacity. Multi-frequency single-transmitter multiple-receiver wireless charging (MF-STMR-WC), designed to minimize the inductive cross-coupling effect, is well-suited for simultaneously charging multiple IoT devices. The key technique for MF-STMR-WC systems is the multi-frequency modulation method. Conventional methods primarily rely on pulsewidth modulation (PWM), offering independent power allocation but involving a high switching frequency. This article proposes a hybrid multi-frequency pulse modulation (HMFPM) method that combines pulsewidth and density modulation. By incorporating pulse density modulation (PDM), the switching frequency decreases, leading to reduced switching losses and improved efficiency. The experimental results verify the effectiveness of the proposed HMFPM method. In comparison to a conventional PWM method with the lowest switching frequency, the proposed method helps attain lower inverter power loss of up to 48.78% and higher power transfer efficiency of up to 7.32%.